What is the ecliptic longitude of the sun at the summer solstice?

The Sun’s ecliptic longitude is 90 degrees at the Northern Hemisphere summer solstice.

Ecliptic longitude measures the Sun’s apparent position along the ecliptic, the path it appears to trace across the sky during the year. Astronomers measure it eastward from the March equinox, defined as 0 degrees. Three months later, at the June solstice, the Sun reaches 90 degrees.

The four seasonal reference points divide the ecliptic into quarter-turns: 0 degrees at the March equinox, 90 degrees at the June solstice, 180 degrees at the September equinox, and 270 degrees at the December solstice. These are coordinate markers, not distances from Earth.

The opposing Southern Hemisphere summer solstice occurs at 270 degrees, which is why specifying the hemisphere matters in technical astronomy. In ordinary Northern Hemisphere usage, however, “the summer solstice” means the June solstice and the canonical answer is 90 degrees.